linux-kernel - [PATCH] Thermal: Fix lockup of cpu

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Message-ID: <1373997748.6458.26.camel@gandalf.local.home>
Date:	Tue, 16 Jul 2013 14:02:28 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Zhang Rui <rui.zhang@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH] Thermal: Fix lockup of cpu_down()

Commit f1a18a105 "Thermal: CPU Package temperature thermal" had code
that did a get_online_cpus(), run a loop and then do a
put_online_cpus(). The problem is that the loop had an error exit that
would skip the put_online_cpus() part.

In the error exit part of the function, it also did a get_online_cpus(),
run a loop and then put_online_cpus(). The only way to get to the error
exit part is with get_online_cpus() already performed. If this error
condition is hit, the system will be prevented from taking CPUs offline.
The process taking the CPU offline will lock up hard.

Removing the get_online_cpus() removes the lockup as the hotplug CPU
refcount is back to zero.

This was bisected with ktest.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/drivers/thermal/x86_pkg_temp_thermal.c b/drivers/thermal/x86_pkg_temp_thermal.c
index 5de56f6..d47624c 100644
--- a/drivers/thermal/x86_pkg_temp_thermal.c
+++ b/drivers/thermal/x86_pkg_temp_thermal.c
@@ -592,7 +592,6 @@ static int __init pkg_temp_thermal_init(void)
 	return 0;

 err_ret:
-	get_online_cpus();
 	for_each_online_cpu(i)
 		put_core_offline(i);
 	put_online_cpus();

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